/*
 * Copyright (C) 2005 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define LOG_TAG "RefBase"
// #define LOG_NDEBUG 0

#include <fcntl.h>

#include <utils/RefBase.h>
#include <utils/Log.h>


#ifndef __unused
#define __unused __attribute__((__unused__))
#endif

// compile with refcounting debugging enabled
#define DEBUG_REFS                      0

// whether ref-tracking is enabled by default, if not, trackMe(true, false)
// needs to be called explicitly
#define DEBUG_REFS_ENABLED_BY_DEFAULT   0

// whether callstack are collected (significantly slows things down)
#define DEBUG_REFS_CALLSTACK_ENABLED    1

// folder where stack traces are saved when DEBUG_REFS is enabled
// this folder needs to exist and be writable
#define DEBUG_REFS_CALLSTACK_PATH       "/data/debug"

// log all reference counting operations
#define PRINT_REFS                      0

// ---------------------------------------------------------------------------

namespace android {

// Observations, invariants, etc:

// By default, obects are destroyed when the last strong reference disappears
// or, if the object never had a strong reference, when the last weak reference
// disappears.
//
// OBJECT_LIFETIME_WEAK changes this behavior to retain the object
// unconditionally until the last reference of either kind disappears.  The
// client ensures that the extendObjectLifetime call happens before the dec
// call that would otherwise have deallocated the object, or before an
// attemptIncStrong call that might rely on it.  We do not worry about
// concurrent changes to the object lifetime.
//
// AttemptIncStrong will succeed if the object has a strong reference, or if it
// has a weak reference and has never had a strong reference.
// AttemptIncWeak really does succeed only if there is already a WEAK
// reference, and thus may fail when attemptIncStrong would succeed.
//
// mStrong is the strong reference count.  mWeak is the weak reference count.
// Between calls, and ignoring memory ordering effects, mWeak includes strong
// references, and is thus >= mStrong.
//
// A weakref_impl holds all the information, including both reference counts,
// required to perform wp<> operations.  Thus these can continue to be performed
// after the RefBase object has been destroyed.
//
// A weakref_impl is allocated as the value of mRefs in a RefBase object on
// construction.
// In the OBJECT_LIFETIME_STRONG case, it is normally deallocated in decWeak,
// and hence lives as long as the last weak reference. (It can also be
// deallocated in the RefBase destructor iff the strong reference count was
// never incremented and the weak count is zero, e.g.  if the RefBase object is
// explicitly destroyed without decrementing the strong count.  This should be
// avoided.) In this case, the RefBase destructor should be invoked from
// decStrong.
// In the OBJECT_LIFETIME_WEAK case, the weakref_impl is always deallocated in
// the RefBase destructor, which is always invoked by decWeak. DecStrong
// explicitly avoids the deletion in this case.
//
// Memory ordering:
// The client must ensure that every inc() call, together with all other
// accesses to the object, happens before the corresponding dec() call.
//
// We try to keep memory ordering constraints on atomics as weak as possible,
// since memory fences or ordered memory accesses are likely to be a major
// performance cost for this code. All accesses to mStrong, mWeak, and mFlags
// explicitly relax memory ordering in some way.
//
// The only operations that are not memory_order_relaxed are reference count
// decrements. All reference count decrements are release operations.  In
// addition, the final decrement leading the deallocation is followed by an
// acquire fence, which we can view informally as also turning it into an
// acquire operation.  (See 29.8p4 [atomics.fences] for details. We could
// alternatively use acq_rel operations for all decrements. This is probably
// slower on most current (2016) hardware, especially on ARMv7, but that may
// not be true indefinitely.)
//
// This convention ensures that the second-to-last decrement synchronizes with
// (in the language of 1.10 in the C++ standard) the final decrement of a
// reference count. Since reference counts are only updated using atomic
// read-modify-write operations, this also extends to any earlier decrements.
// (See "release sequence" in 1.10.)
//
// Since all operations on an object happen before the corresponding reference
// count decrement, and all reference count decrements happen before the final
// one, we are guaranteed that all other object accesses happen before the
// object is destroyed.


#define INITIAL_STRONG_VALUE (1<<28)

#define MAX_COUNT 0xfffff

// Test whether the argument is a clearly invalid strong reference count.
// Used only for error checking on the value before an atomic decrement.
// Intended to be very cheap.
// Note that we cannot just check for excess decrements by comparing to zero
// since the object would be deallocated before that.
#define BAD_STRONG(c) \
        ((c) == 0 || ((c) & (~(MAX_COUNT | INITIAL_STRONG_VALUE))) != 0)

// Same for weak counts.
#define BAD_WEAK(c) ((c) == 0 || ((c) & (~MAX_COUNT)) != 0)

// ---------------------------------------------------------------------------

    class RefBase::weakref_impl : public RefBase::weakref_type {
    public:
        std::atomic<int32_t> mStrong;
        std::atomic<int32_t> mWeak;
        RefBase *const mBase;
        std::atomic<int32_t> mFlags;

#if !DEBUG_REFS

        explicit weakref_impl(RefBase *base)
                : mStrong(INITIAL_STRONG_VALUE), mWeak(0), mBase(base), mFlags(0) {
        }

        void addStrongRef(const void * /*id*/) {}

        void removeStrongRef(const void * /*id*/) {}

        void renameStrongRefId(const void * /*old_id*/, const void * /*new_id*/) {}

        void addWeakRef(const void * /*id*/) {}

        void removeWeakRef(const void * /*id*/) {}

        void renameWeakRefId(const void * /*old_id*/, const void * /*new_id*/) {}

        void printRefs() const {}

        void trackMe(bool, bool) {}

#else

        weakref_impl(RefBase* base)
            : mStrong(INITIAL_STRONG_VALUE)
            , mWeak(0)
            , mBase(base)
            , mFlags(0)
            , mStrongRefs(NULL)
            , mWeakRefs(NULL)
            , mTrackEnabled(!!DEBUG_REFS_ENABLED_BY_DEFAULT)
            , mRetain(false)
        {
        }

        ~weakref_impl()
        {
            bool dumpStack = false;
            if (!mRetain && mStrongRefs != NULL) {
                dumpStack = true;
                ALOGE("Strong references remain:");
                ref_entry* refs = mStrongRefs;
                while (refs) {
                    char inc = refs->ref >= 0 ? '+' : '-';
                    ALOGD("\t%c ID %p (ref %d):", inc, refs->id, refs->ref);
#if DEBUG_REFS_CALLSTACK_ENABLED
                    refs->stack.log(LOG_TAG);
#endif
                    refs = refs->next;
                }
            }

            if (!mRetain && mWeakRefs != NULL) {
                dumpStack = true;
                ALOGE("Weak references remain!");
                ref_entry* refs = mWeakRefs;
                while (refs) {
                    char inc = refs->ref >= 0 ? '+' : '-';
                    ALOGD("\t%c ID %p (ref %d):", inc, refs->id, refs->ref);
#if DEBUG_REFS_CALLSTACK_ENABLED
                    refs->stack.log(LOG_TAG);
#endif
                    refs = refs->next;
                }
            }
            if (dumpStack) {
                ALOGE("above errors at:");
                CallStack stack(LOG_TAG);
            }
        }

        void addStrongRef(const void* id) {
            //ALOGD_IF(mTrackEnabled,
            //        "addStrongRef: RefBase=%p, id=%p", mBase, id);
            addRef(&mStrongRefs, id, mStrong.load(std::memory_order_relaxed));
        }

        void removeStrongRef(const void* id) {
            //ALOGD_IF(mTrackEnabled,
            //        "removeStrongRef: RefBase=%p, id=%p", mBase, id);
            if (!mRetain) {
                removeRef(&mStrongRefs, id);
            } else {
                addRef(&mStrongRefs, id, -mStrong.load(std::memory_order_relaxed));
            }
        }

        void renameStrongRefId(const void* old_id, const void* new_id) {
            //ALOGD_IF(mTrackEnabled,
            //        "renameStrongRefId: RefBase=%p, oid=%p, nid=%p",
            //        mBase, old_id, new_id);
            renameRefsId(mStrongRefs, old_id, new_id);
        }

        void addWeakRef(const void* id) {
            addRef(&mWeakRefs, id, mWeak.load(std::memory_order_relaxed));
        }

        void removeWeakRef(const void* id) {
            if (!mRetain) {
                removeRef(&mWeakRefs, id);
            } else {
                addRef(&mWeakRefs, id, -mWeak.load(std::memory_order_relaxed));
            }
        }

        void renameWeakRefId(const void* old_id, const void* new_id) {
            renameRefsId(mWeakRefs, old_id, new_id);
        }

        void trackMe(bool track, bool retain)
        {
            mTrackEnabled = track;
            mRetain = retain;
        }

        void printRefs() const
        {
            String8 text;

            {
                Mutex::Autolock _l(mMutex);
                char buf[128];
                snprintf(buf, sizeof(buf),
                         "Strong references on RefBase %p (weakref_type %p):\n",
                         mBase, this);
                text.append(buf);
                printRefsLocked(&text, mStrongRefs);
                snprintf(buf, sizeof(buf),
                         "Weak references on RefBase %p (weakref_type %p):\n",
                         mBase, this);
                text.append(buf);
                printRefsLocked(&text, mWeakRefs);
            }

            {
                char name[100];
                snprintf(name, sizeof(name), DEBUG_REFS_CALLSTACK_PATH "/%p.stack",
                         this);
                int rc = open(name, O_RDWR | O_CREAT | O_APPEND, 644);
                if (rc >= 0) {
                    write(rc, text.string(), text.length());
                    close(rc);
                    ALOGD("STACK TRACE for %p saved in %s", this, name);
                }
                else ALOGE("FAILED TO PRINT STACK TRACE for %p in %s: %s", this,
                          name, strerror(errno));
            }
        }

    private:
        struct ref_entry
        {
            ref_entry* next;
            const void* id;
#if DEBUG_REFS_CALLSTACK_ENABLED
            CallStack stack;
#endif
            int32_t ref;
        };

        void addRef(ref_entry** refs, const void* id, int32_t mRef)
        {
            if (mTrackEnabled) {
                AutoMutex _l(mMutex);

                ref_entry* ref = new ref_entry;
                // Reference count at the time of the snapshot, but before the
                // update.  Positive value means we increment, negative--we
                // decrement the reference count.
                ref->ref = mRef;
                ref->id = id;
#if DEBUG_REFS_CALLSTACK_ENABLED
                ref->stack.update(2);
#endif
                ref->next = *refs;
                *refs = ref;
            }
        }

        void removeRef(ref_entry** refs, const void* id)
        {
            if (mTrackEnabled) {
                AutoMutex _l(mMutex);

                ref_entry* const head = *refs;
                ref_entry* ref = head;
                while (ref != NULL) {
                    if (ref->id == id) {
                        *refs = ref->next;
                        delete ref;
                        return;
                    }
                    refs = &ref->next;
                    ref = *refs;
                }

                ALOGE("RefBase: removing id %p on RefBase %p"
                        "(weakref_type %p) that doesn't exist!",
                        id, mBase, this);

                ref = head;
                while (ref) {
                    char inc = ref->ref >= 0 ? '+' : '-';
                    ALOGD("\t%c ID %p (ref %d):", inc, ref->id, ref->ref);
                    ref = ref->next;
                }

                CallStack stack(LOG_TAG);
            }
        }

        void renameRefsId(ref_entry* r, const void* old_id, const void* new_id)
        {
            if (mTrackEnabled) {
                AutoMutex _l(mMutex);
                ref_entry* ref = r;
                while (ref != NULL) {
                    if (ref->id == old_id) {
                        ref->id = new_id;
                    }
                    ref = ref->next;
                }
            }
        }

        void printRefsLocked(String8* out, const ref_entry* refs) const
        {
            char buf[128];
            while (refs) {
                char inc = refs->ref >= 0 ? '+' : '-';
                snprintf(buf, sizeof(buf), "\t%c ID %p (ref %d):\n",
                         inc, refs->id, refs->ref);
                out->append(buf);
#if DEBUG_REFS_CALLSTACK_ENABLED
                out->append(refs->stack.toString("\t\t"));
#else
                out->append("\t\t(call stacks disabled)");
#endif
                refs = refs->next;
            }
        }

        mutable Mutex mMutex;
        ref_entry* mStrongRefs;
        ref_entry* mWeakRefs;

        bool mTrackEnabled;
        // Collect stack traces on addref and removeref, instead of deleting the stack references
        // on removeref that match the address ones.
        bool mRetain;

#endif
    };

// ---------------------------------------------------------------------------

    void RefBase::incStrong(const void *id) const {
        weakref_impl *const refs = mRefs;
        refs->incWeak(id);

        refs->addStrongRef(id);
        const int32_t c = refs->mStrong.fetch_add(1, std::memory_order_relaxed);
        LOG_ASSERT(c > 0, "incStrong() called on %p after last strong ref", refs);
#if PRINT_REFS
        ALOGD("incStrong of %p from %p: cnt=%d\n", this, id, c);
#endif
        if (c != INITIAL_STRONG_VALUE) {
            return;
        }

        int32_t old = refs->mStrong.fetch_sub(INITIAL_STRONG_VALUE,
                                              std::memory_order_relaxed);
        // A decStrong() must still happen after us.
        LOG_ASSERT(old > INITIAL_STRONG_VALUE, "0x%x too small", old);
        refs->mBase->onFirstRef();
    }

    void RefBase::decStrong(const void *id) const {
        weakref_impl *const refs = mRefs;
        refs->removeStrongRef(id);
        const int32_t c = refs->mStrong.fetch_sub(1, std::memory_order_release);
#if PRINT_REFS
        ALOGD("decStrong of %p from %p: cnt=%d\n", this, id, c);
#endif
        LOG_ALWAYS_FATAL_IF(BAD_STRONG(c), "decStrong() called on %p too many times",
                            refs);
        if (c == 1) {
            std::atomic_thread_fence(std::memory_order_acquire);
            refs->mBase->onLastStrongRef(id);
            int32_t flags = refs->mFlags.load(std::memory_order_relaxed);
            if ((flags & OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_STRONG) {
                delete this;
                // The destructor does not delete refs in this case.
            }
        }
        // Note that even with only strong reference operations, the thread
        // deallocating this may not be the same as the thread deallocating refs.
        // That's OK: all accesses to this happen before its deletion here,
        // and all accesses to refs happen before its deletion in the final decWeak.
        // The destructor can safely access mRefs because either it's deleting
        // mRefs itself, or it's running entirely before the final mWeak decrement.
        refs->decWeak(id);
    }

    void RefBase::forceIncStrong(const void *id) const {
        // Allows initial mStrong of 0 in addition to INITIAL_STRONG_VALUE.
        // TODO: Better document assumptions.
        weakref_impl *const refs = mRefs;
        refs->incWeak(id);

        refs->addStrongRef(id);
        const int32_t c = refs->mStrong.fetch_add(1, std::memory_order_relaxed);
        LOG_ASSERT(c >= 0, "forceIncStrong called on %p after ref count underflow",
                   refs);
#if PRINT_REFS
        ALOGD("forceIncStrong of %p from %p: cnt=%d\n", this, id, c);
#endif

        switch (c) {
            case INITIAL_STRONG_VALUE:
                refs->mStrong.fetch_sub(INITIAL_STRONG_VALUE,
                                        std::memory_order_relaxed);
                // fall through...
            case 0:
                refs->mBase->onFirstRef();
        }
    }

    int32_t RefBase::getStrongCount() const {
        // Debugging only; No memory ordering guarantees.
        return mRefs->mStrong.load(std::memory_order_relaxed);
    }

    RefBase *RefBase::weakref_type::refBase() const {
        return static_cast<const weakref_impl *>(this)->mBase;
    }

    void RefBase::weakref_type::incWeak(const void *id) {
        weakref_impl *const impl = static_cast<weakref_impl *>(this);
        impl->addWeakRef(id);
        const int32_t c __unused = impl->mWeak.fetch_add(1,
                                                         std::memory_order_relaxed);
        LOG_ASSERT(c >= 0, "incWeak called on %p after last weak ref", this);
    }


    void RefBase::weakref_type::decWeak(const void *id) {
        weakref_impl *const impl = static_cast<weakref_impl *>(this);
        impl->removeWeakRef(id);
        const int32_t c = impl->mWeak.fetch_sub(1, std::memory_order_release);
        LOG_ALWAYS_FATAL_IF(BAD_WEAK(c), "decWeak called on %p too many times",
                            this);
        if (c != 1) return;
        atomic_thread_fence(std::memory_order_acquire);

        int32_t flags = impl->mFlags.load(std::memory_order_relaxed);
        if ((flags & OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_STRONG) {
            // This is the regular lifetime case. The object is destroyed
            // when the last strong reference goes away. Since weakref_impl
            // outlives the object, it is not destroyed in the dtor, and
            // we'll have to do it here.
            if (impl->mStrong.load(std::memory_order_relaxed)
                == INITIAL_STRONG_VALUE) {
                // Decrementing a weak count to zero when object never had a strong
                // reference.  We assume it acquired a weak reference early, e.g.
                // in the constructor, and will eventually be properly destroyed,
                // usually via incrementing and decrementing the strong count.
                // Thus we no longer do anything here.  We log this case, since it
                // seems to be extremely rare, and should not normally occur. We
                // used to deallocate mBase here, so this may now indicate a leak.
                ALOGW("RefBase: Object at %p lost last weak reference "
                              "before it had a strong reference", impl->mBase);
            } else {
                // ALOGV("Freeing refs %p of old RefBase %p\n", this, impl->mBase);
                delete impl;
            }
        } else {
            // This is the OBJECT_LIFETIME_WEAK case. The last weak-reference
            // is gone, we can destroy the object.
            impl->mBase->onLastWeakRef(id);
            delete impl->mBase;
        }
    }

    bool RefBase::weakref_type::attemptIncStrong(const void *id) {
        incWeak(id);

        weakref_impl *const impl = static_cast<weakref_impl *>(this);
        int32_t curCount = impl->mStrong.load(std::memory_order_relaxed);

        LOG_ASSERT(curCount >= 0,
                   "attemptIncStrong called on %p after underflow", this);

        while (curCount > 0 && curCount != INITIAL_STRONG_VALUE) {
            // we're in the easy/common case of promoting a weak-reference
            // from an existing strong reference.
            if (impl->mStrong.compare_exchange_weak(curCount, curCount + 1,
                                                    std::memory_order_relaxed)) {
                break;
            }
            // the strong count has changed on us, we need to re-assert our
            // situation. curCount was updated by compare_exchange_weak.
        }

        if (curCount <= 0 || curCount == INITIAL_STRONG_VALUE) {
            // we're now in the harder case of either:
            // - there never was a strong reference on us
            // - or, all strong references have been released
            int32_t flags = impl->mFlags.load(std::memory_order_relaxed);
            if ((flags & OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_STRONG) {
                // this object has a "normal" life-time, i.e.: it gets destroyed
                // when the last strong reference goes away
                if (curCount <= 0) {
                    // the last strong-reference got released, the object cannot
                    // be revived.
                    decWeak(id);
                    return false;
                }

                // here, curCount == INITIAL_STRONG_VALUE, which means
                // there never was a strong-reference, so we can try to
                // promote this object; we need to do that atomically.
                while (curCount > 0) {
                    if (impl->mStrong.compare_exchange_weak(curCount, curCount + 1,
                                                            std::memory_order_relaxed)) {
                        break;
                    }
                    // the strong count has changed on us, we need to re-assert our
                    // situation (e.g.: another thread has inc/decStrong'ed us)
                    // curCount has been updated.
                }

                if (curCount <= 0) {
                    // promote() failed, some other thread destroyed us in the
                    // meantime (i.e.: strong count reached zero).
                    decWeak(id);
                    return false;
                }
            } else {
                // this object has an "extended" life-time, i.e.: it can be
                // revived from a weak-reference only.
                // Ask the object's implementation if it agrees to be revived
                if (!impl->mBase->onIncStrongAttempted(FIRST_INC_STRONG, id)) {
                    // it didn't so give-up.
                    decWeak(id);
                    return false;
                }
                // grab a strong-reference, which is always safe due to the
                // extended life-time.
                curCount = impl->mStrong.fetch_add(1, std::memory_order_relaxed);
                // If the strong reference count has already been incremented by
                // someone else, the implementor of onIncStrongAttempted() is holding
                // an unneeded reference.  So call onLastStrongRef() here to remove it.
                // (No, this is not pretty.)  Note that we MUST NOT do this if we
                // are in fact acquiring the first reference.
                if (curCount != 0 && curCount != INITIAL_STRONG_VALUE) {
                    impl->mBase->onLastStrongRef(id);
                }
            }
        }

        impl->addStrongRef(id);

#if PRINT_REFS
        ALOGD("attemptIncStrong of %p from %p: cnt=%d\n", this, id, curCount);
#endif

        // curCount is the value of mStrong before we incremented it.
        // Now we need to fix-up the count if it was INITIAL_STRONG_VALUE.
        // This must be done safely, i.e.: handle the case where several threads
        // were here in attemptIncStrong().
        // curCount > INITIAL_STRONG_VALUE is OK, and can happen if we're doing
        // this in the middle of another incStrong.  The subtraction is handled
        // by the thread that started with INITIAL_STRONG_VALUE.
        if (curCount == INITIAL_STRONG_VALUE) {
            impl->mStrong.fetch_sub(INITIAL_STRONG_VALUE,
                                    std::memory_order_relaxed);
        }

        return true;
    }

    bool RefBase::weakref_type::attemptIncWeak(const void *id) {
        weakref_impl *const impl = static_cast<weakref_impl *>(this);

        int32_t curCount = impl->mWeak.load(std::memory_order_relaxed);
        LOG_ASSERT(curCount >= 0, "attemptIncWeak called on %p after underflow",
                   this);
        while (curCount > 0) {
            if (impl->mWeak.compare_exchange_weak(curCount, curCount + 1,
                                                  std::memory_order_relaxed)) {
                break;
            }
            // curCount has been updated.
        }

        if (curCount > 0) {
            impl->addWeakRef(id);
        }

        return curCount > 0;
    }

    int32_t RefBase::weakref_type::getWeakCount() const {
        // Debug only!
        return static_cast<const weakref_impl *>(this)->mWeak
                .load(std::memory_order_relaxed);
    }

    void RefBase::weakref_type::printRefs() const {
        static_cast<const weakref_impl *>(this)->printRefs();
    }

    void RefBase::weakref_type::trackMe(bool enable, bool retain) {
        static_cast<weakref_impl *>(this)->trackMe(enable, retain);
    }

    RefBase::weakref_type *RefBase::createWeak(const void *id) const {
        mRefs->incWeak(id);
        return mRefs;
    }

    RefBase::weakref_type *RefBase::getWeakRefs() const {
        return mRefs;
    }

    RefBase::RefBase()
            : mRefs(new weakref_impl(this)) {
    }

    RefBase::~RefBase() {
        int32_t flags = mRefs->mFlags.load(std::memory_order_relaxed);
        // Life-time of this object is extended to WEAK, in
        // which case weakref_impl doesn't out-live the object and we
        // can free it now.
        if ((flags & OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_WEAK) {
            // It's possible that the weak count is not 0 if the object
            // re-acquired a weak reference in its destructor
            if (mRefs->mWeak.load(std::memory_order_relaxed) == 0) {
                delete mRefs;
            }
        } else if (mRefs->mStrong.load(std::memory_order_relaxed)
                   == INITIAL_STRONG_VALUE) {
            // We never acquired a strong reference on this object.
            LOG_ALWAYS_FATAL_IF(mRefs->mWeak.load() != 0,
                                "RefBase: Explicit destruction with non-zero weak "
                                        "reference count");
            // TODO: Always report if we get here. Currently MediaMetadataRetriever
            // C++ objects are inconsistently managed and sometimes get here.
            // There may be other cases, but we believe they should all be fixed.
            delete mRefs;
        }
        // For debugging purposes, clear mRefs.  Ineffective against outstanding wp's.
        const_cast<weakref_impl *&>(mRefs) = NULL;
    }

    void RefBase::extendObjectLifetime(int32_t mode) {
        // Must be happens-before ordered with respect to construction or any
        // operation that could destroy the object.
        mRefs->mFlags.fetch_or(mode, std::memory_order_relaxed);
    }

    void RefBase::onFirstRef() {
    }

    void RefBase::onLastStrongRef(const void * /*id*/) {
    }

    bool RefBase::onIncStrongAttempted(uint32_t flags, const void * /*id*/) {
        return (flags & FIRST_INC_STRONG) ? true : false;
    }

    void RefBase::onLastWeakRef(const void * /*id*/) {
    }

// ---------------------------------------------------------------------------

#if DEBUG_REFS
    void RefBase::renameRefs(size_t n, const ReferenceRenamer& renamer) {
        for (size_t i=0 ; i<n ; i++) {
            renamer(i);
        }
    }
#else

    void RefBase::renameRefs(size_t /*n*/, const ReferenceRenamer & /*renamer*/) {}

#endif

    void RefBase::renameRefId(weakref_type *ref,
                              const void *old_id, const void *new_id) {
        weakref_impl *const impl = static_cast<weakref_impl *>(ref);
        impl->renameStrongRefId(old_id, new_id);
        impl->renameWeakRefId(old_id, new_id);
    }

    void RefBase::renameRefId(RefBase *ref,
                              const void *old_id, const void *new_id) {
        ref->mRefs->renameStrongRefId(old_id, new_id);
        ref->mRefs->renameWeakRefId(old_id, new_id);
    }

    VirtualLightRefBase::~VirtualLightRefBase() {}

}; // namespace android
